Stretch wrap or stretch film is a highly stretchable plastic film that is wrapped around items. The elastic recovery keeps the items tightly bound. In contrast, shrink wrap is applied loosely around an item and shrinks tightly with heat.
It is frequently used to unitize pallet loads but also may be used for bundling smaller items.
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Materials
The most common stretch wrap material is linear low-density polyethylene or LLDPE, which is produced by copolymerization of ethylene with alpha-olefins, the most common of which are butene, hexene and octene. The use of higher alpha-olefins (hexene or octene) gives rise to enhanced stretch film characteristics, particularly in respect of elongation at break and puncture resistance. Other types of polyethylene and PVC can also be used. Many films have about 500% stretch at break but are only stretched to about 100 – 300% in use. Once stretched, the elastic recovery is used to keep the load tight.
Other properties such as break strength, cling, clarity, tear resistance, static discharge, etc. are also important.
Functions
In pallet unitizing, stretch wrap can have several functions:
- improved stability of products or packages, forming a unit load
- more efficient handling and storage of unit loads
- some degree of dust and moisture protection
- some degree of tamper resistance and resistance to package pilferage
Making sure cartons stay on the pallet is an important consideration in warehouse distribution, especially as the demands for increased throughput continues to rise. Stretch wrapping is the most cost-effective way to keep loads secured on a pallet. [1]
Application
Stretch wrap can be applied manually with small rolls (perhaps 5-inch wide) of film. Dispensers are also available for larger rolls (perhaps 12 – 15 inch wide).
Machinery is available to automate the operation. This controls the amount of material used, controls the stretch, and controls the application pattern.
It is important not to apply too much tension or too many layers: the stress can damage the vertical edges of the boxes and significantly reduce stacking strength.
References
See also
Further reading
- ASTM International D4649 Guide for Selection and Use of Stretch Wrap Films
- Brody, A. L., and Marsh, K, S., "Encyclopedia of Packaging Technology", John Wiley & Sons, 1997, ISBN 0-471-06397-5
- M.Hindreth, "Maximizing your Stretch Film Operation", 2006, ISTA, Pre Shipment Testing, [1]
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